1. Field of the Invention
The present general inventive concept relates to a method and apparatus to control the fusing temperature of an image forming apparatus, and, more particularly, to a method and apparatus to control the fusing temperature of an image forming apparatus that adjusts a fusing temperature and a fan flow rate as the number of sheets of paper printed continuously increases.
2. Description of the Related Art
An electrophotographic image forming apparatus includes a fixing apparatus, which heats a sheet of paper having a toner image transferred, fuses the toner image in a powder state, and fixes the toner image on the sheet of paper. The fixing apparatus includes a fusing roller for fixing toner on the sheet of paper and a pressure roller for pressing the sheet of paper against the fusing roller.
FIG. 1 is a horizontal sectional view of a conventional fusing roller using a halogen lamp as a heat source. FIG. 2 is a vertical sectional view of a fixing apparatus adopting the fusing roller shown in FIG. 1.
Referring to FIG. 1, the fusing roller 10 includes a cylindrical roller 11 and a halogen lamp 12 installed in the middle of the cylindrical roller 11. A teflon coating layer 11 a is formed on the surface of the cylindrical roller 11. The halogen lamp 12 generates heat inside the cylindrical roller 11, and the cylindrical roller 11 is heated by radiant heat from the halogen lamp 11.
Referring to FIG. 2, a pressure roller 13 facing the cylindrical roller 11 is placed on the bottom of the fusing roller 10 interposing a sheet of paper 14 therebetween. Supported elastically by a spring 13a, the pressure roller 13 pushes the sheet of paper 14, which passes between the fusing roller 10 and the pressure roller 13, toward the fusing roller 10 with predetermined pressure. Here, a powder-state toner image 14a, which was transferred on the sheet of paper 14, is fixed on the sheet of paper 14 by predetermined pressure and heat when the sheet of paper 14 passes between the fusing roller 10 and the pressure roller 13.
Installed on one side of the fusing roller 10 are a thermistor 15 for measuring the surface temperature of the fusing roller 10 and a thermostat 16 for cutting off the supply of power to the halogen lamp 12 when the surface temperature of the fusing roller 10 exceeds a set value. The thermistor 15 measures the surface temperature of the fusing roller 10 and transmits an electric signal of the measured temperature to a control unit (not shown) of a printer (not shown). Then, the control unit controls power to be supplied to the halogen lamp 12 according to the measured temperature and maintains the surface temperature of the fusing roller 10 within a predetermined range. Furthermore, when the control unit fails to control the surface temperature of the fusing roller 10, leading the temperature of the fusing roller 10 to a temperature higher than a set limit value, a contact (not shown) of the thermostat 16 is opened to cut off power supplied to the halogen lamp 12.
In the meantime, in case of printing continuously while maintaining the fusing temperature of the fusing roller 10 within a predetermined range, the ambient temperature of the fusing roller 10 increases due to the heat generated from the fusing roller 10. In particular, an increase in the temperature of the pressure roller 13 directly leads to an increase in the temperature of the paper passing over the pressing roller 13, which is a major cause of paper creases.
Inside the image forming apparatus is installed a fan, which exhausts hot air to the outside (externally) to lower the internal temperature. The fan cools the inside of the printer to prevent overheating. However, the fan also accelerates the flow of air inside the image forming apparatus, thereby also forming creases in the paper. In particular, more creases in the paper are formed when the temperature of paper is higher than an appropriate fusing temperature.
In order to control a fusing temperature, there has been proposed a method of measuring the temperature of a fusing roller 10 and adjusting the heat from a halogen lamp 12 being a heat source.
However, this method, intended to maintain the temperature of a fusing roller 10 steadily, fails to prevent the creasing of paper because the ambient temperature of the fixing apparatus including a pressure roller 13 rises as a result of a continued use of a printer.